tools: fix doc generation when version info is not available

Fixes: https://github.com/nodejs/node/issues/38391

PR-URL: https://github.com/nodejs/node/pull/38398


Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>